Research On Single-lens Large Depth-of-field Machine Vision Inspection Technology Based On Dispersion

Machine vision inspection technology is a modern technology that applies a camera to acquire images of the targets and analyzes the quality of the targets through these images.In the face of the ever increasing labor costs,this non-contact detection technology has become an important method for many companies to increase production efficiency and reduce production costs.However,for some large size targets,traditional machine vision systems are limited by the depth-of-field and can't effectively complete inspection tasks.Therefore,we researched the single-lens large depth-of-field machine vision inspection technology based on dispersion:1?We studied the depth-of-field and the dispersion of a single-lens imaging system.Factors influencing the depth-of-field were also discussed.To enlarge the depth-of-field of single-lens system,the discrete spectral illumination approach based on imaging dispersion was proposed.A positive correlation between the object distance and the wavelength of the illumination light was theoretically derived.According to this relation,light sources with suitable wavelengths were selected.Through the illumination optical design,objects with different object distances can be imaged on the same image plane.The simulation results obtained by ZEMAX are consistent with the theoretical analysis.An image acquisition system using biconvex lens was designed for practical measurement,and a biconvex lens with focus of 35 mm was used in the experiments.Both human subjective and professional software test results show that sub-band illumination can effectively extend the depth of field.2?We also designed a program-controlled light source to solve the illumination problem caused by multiple groups of LEDs.Several independent step-down DC/DC modules were used to supply LEDs.The brightness of all LEDs could be adjusted by PWM wave.We used an Arduino module to communicate between computer and the light source module.Therefore,in the computer,we could control the multiple groups of LEDs independently to make the illumination of target suitable.3 ? A single-lens large depth-of-field machine vision inspection system based on dispersion was built.The system uses discrete spectral illumination approach to achieve a large depth-of-field imaging of a large size target at one time.Meanwhile,the program-controlled light source was used to achieve partitioned lighting of the target surface.In order to apply the system to practice,we studied the flaw inspection program.Firstly,we preprocessed the target image to enhance the contrast.Secondly,the threshold recognition and other methods were used to detect flaws.The experimental results show that the system can effectively detect the simulated scratches with a minimum width of 0.0875 mm and the simulated fouling with a minimum diameter of 0.304 mm within 250 mm depth-of-field.The single-lens large depth-of-field machine vision inspection system can effectively detect flaws of large size targets.The system can save time and improve the detection efficiency to reduce the production cost.